yeah this seems like a small but big problem . It really depends on her personality , some people deny they are ever wrong in order to seem perfect or always right . This is sometimes a big problem and can be a bad thing in a relationship , I suggest that you talk to her and try to listen to her explain and then tell her how you feel about it . Even though you may still really like or love your girlfriend you need to work out this misunderstanding to have a better relationship , don't yell at her or have a big fit about how shes not always right , sit down with her and tell her how you feel about this , you guys are in a relationship so unless shes always going to do that , then maybe taking a break is a good idea , that is if she always denies shes wrong to big problems , if they small things like eg. What does your mom want for chrismas or something , that isn't too bad but make sure you communicate with her and ignore this .